1. Field of the Invention
The present invention concerns a control device for a hydraulic actuator for use in steering, for example, an aircraft, and it relates to a control device for a hydraulic actuator used in steering which is capable of attaining complicated steering characteristics such as non-linear characteristics, with a simple circuit, and easily changing the characteristics with no requirement for the change of the circuit itself.
2. Description of the Prior Art
For reducing the manipulating force required for turning a steering wheel, a so-called steering system using a hydraulic actuator as a power assist has been commonly employed.
The power steering control is provided by a position servo mechanism based on the operation of a steering wheel as an input and an angular displacement of a vehicle wheel as an output. In view of the mechanism, its construction is of the integral type having a hydraulic actuator and a control valve contained in a gear box. A linkage unit houses the actuator, valve, and gear box in a lump in a booster unit which is disposed, for example, at the midway of a steering link mechanism. A spool or rotary type valve is used as the control valve, and an open center valve system that causes no hydraulic pressure unless the steering wheel is operated, is used for either type of valve.
In addition to the construction described above in which the steering wheel and the steering link mechanism are connected mechanically, a steering mechanism is also known for use, for example, in an aircraft, in which a steering wheel is separated from a vehicle wheel. An actuator is operated in accordance with an aimed angle of the wheel indicated, for example, by a potentiometer or the like connected to the steering wheel, thereby rotating the wheel by way of a link mechanism.
In the steering mechanism as described above, a control device of the actuator determines the directional accuracy of a vehicle wheel. A control device in the prior art has such a construction that a desired angle of a vehicle wheel, that is, a desired positional signal indicated by a potentiometer or the like connected to a steering wheel, and a feedback (FB) signal from a potentiometer or the like indicating an actual angle of the vehicle wheel or an actual position of an actuator for operating the vehicle, are inputted and a signal for operating the actuator to turn the vehicle wheel to the desired angle is outputted. An analog circuit having operation amplifiers such as a summing circuit 20 and an output circuit 21 combined as shown in FIG. 3 (A) are used for calculating an output in accordance with the input.
Steering mechanisms wherein the steering wheel is separated from the vehicle wheel and the actuator are different from a mechanical connection and have no steering characteristics on the side of the steering wheel unit. Thus, such characteristics have to be provided to the actuator.
In the control device of the actuator, however, if it is intended to furnish an analog circuit with such steering characteristics as free play characteristics, step characteristics and non-linear characteristics, the circuit will require an idle steering generating circuit 22, a step characteristic generating circuit 23, and a non-linear characteristic generating circuit 24, as shown in FIG. 3B, resulting in a complicated circuit structure.
In addition, if the steering characteristics are to be changed, even a little, the circuit itself has to be changed.